JP4767129B2 - OS switching device and OS switching method - Google Patents

Description

  The present invention relates to an OS switching device and an OS switching method.

Conventionally, a technique for separating a single code into an execution part at the user level (protection mode) and an execution part at the kernel level (non-protection mode) has been proposed (see, for example, Patent Document 1). In this technique, critical code is obfuscated from the debugger by executing critical code in a kernel exception handler, thereby obfuscating the code.
US 2003/0093685 A1

  However, in the above Patent Document 1, the effect is limited to the function of preventing execution processes in the userland from reading the code in the kernel within a single OS, and in a multi-OS environment in which multiple OSs operate. Attacks on other operating systems cannot be prevented.

  Therefore, in view of the above problems, the present invention has an object to provide an OS switching device and an OS switching method that protect against attacks of reading confidential information and falsification from one OS to another OS in a multi-OS environment. And

  In order to achieve the above object, a first feature of the present invention is that a plurality of OSs including an OS stop unit that stops an OS and an OS start unit that restarts execution of the OS, and the plurality of OSs are switched to operate. An OS switching device comprising: an OS switching unit for executing: (a) an exception processing unit that performs exception processing; (b) a secret generation unit that generates a secret used to implement a security function; and (c) exception processing. The gist of the invention is that the OS switching device includes a secret calculation unit that is mounted in the unit and executes a secret calculation.

  According to the OS switching device according to the first feature, in a multi-OS environment, it is possible to prevent an attack of reading confidential information from one OS or the other OS and falsification.

  In the OS switching device according to the first feature, the OS includes a confidential information holding unit that stores confidential information, and an encryption / decryption unit that encrypts and decrypts the confidential information stored in the confidential information holding unit. And a key generation unit that generates an encryption key to be used by the encryption / decryption unit using the secret calculated by the secret calculation unit.

  According to this OS switching device, when generating a secret (pseudo random number data) in the secret generation unit held in the OS, it is difficult to reproduce by the attacking OS by performing an operation on the secret in the exception processing unit of the OS A secret can be generated.

  In the OS switching device according to the first feature, the OS may further include an integrity verification unit that verifies the integrity of data or code.

  According to this OS switching device, the integrity of data or code can be further improved.

  In the OS switching device, the OS switching unit includes a confidential information holding unit that stores confidential information, and an encryption / decryption unit that encrypts and decrypts the confidential information stored in the confidential information holding unit. Further, a key generation unit that generates an encryption key used by the encryption / decryption unit using the secret calculated by the secret calculation unit may be further provided.

  According to this OS switching device, when the secret (pseudo random number data) is generated in the secret generation unit held in the OS switching unit, it is reproduced by the attacking OS by performing an operation on the secret in the exception processing unit of the OS switching unit Can generate a difficult secret.

  In the OS switching device, the OS switching unit may further include an integrity verification unit that verifies the integrity of data or code.

  According to this OS switching device, the integrity of data or code can be further improved.

  The OS switching device may further include a duplicate memory management unit that maps a plurality of secret generation units to the virtual address space of the memory.

  According to this OS switching device, it is possible to make the reproduction of the secret more difficult by mapping the original data used when generating the secret to a plurality of locations on the virtual memory and specifying the location away from the specific register. .

  The OS switching device may further include an absolute memory address management unit that specifies data using an absolute memory address when the secret generation unit acquires data for generating a secret.

  According to this OS switching device, by specifying the original data for generating the secret using the alias on the virtual memory, the reproduction of the secret can be made more difficult and the safety can be further improved.

  The OS switching device according to the first feature may further include a read-only storage unit that stores data and codes.

  According to this OS switching device, it is possible to prevent tampering attacks by executing secret generation and encryption processing from ROM.

  The OS switching device according to the first feature may further include a failure recovery unit that detects falsification and recovers to a normal state.

  According to this OS switching device, by recovering from the ROM when a tampering or failure is detected, it is possible to increase resistance against not only reading by the attacking OS but also a tampering attack.

  In the OS switching device, the OS may further include an integrity verification unit that verifies the integrity of the OS switching unit.

  This OS switching device can further enhance the integrity of the OS switching unit.

  In the OS switching device, the OS switching unit may further include an integrity verification unit that verifies the integrity of the OS.

  This OS switching device can further enhance the integrity of the OS.

  The OS switching device according to the first feature may further include a hardware assist obfuscation unit that performs hardware assist obfuscation using the secret calculated by the secret calculation unit.

  According to this OS switching device, the security can be further improved by using a secret that is difficult for the attacking OS to reproduce for hardware-assisted obfuscation.

  A second feature of the present invention is an OS switching method for switching control from one OS to another OS in an OS switching device including a plurality of OSs and an OS switching unit that switches and operates the plurality of OSs. (A) generating a secret used for realizing the security function; (b) executing an operation of the secret in the exception processing unit that performs the exception processing; and (c) using the calculated secret. The gist of the present invention is an OS switching method including the step of encrypting confidential information or the entire memory in the OS.

  According to the OS switching method according to the second feature, in a multi-OS environment, it is possible to prevent an attack of reading confidential information or falsification from one OS to the other OS.

  According to the present invention, it is possible to provide an OS switching device and an OS switching method that protect against attacks of reading confidential information from one OS to the other OS and tampering in a multi-OS environment.

  Next, embodiments of the present invention will be described with reference to the drawings. In the following description of the drawings, the same or similar parts are denoted by the same or similar reference numerals. However, it should be noted that the drawings are schematic.

(OS switching device)
First, the OS switching device according to the present embodiment will be described with reference to FIGS. 1 and 2.

  FIG. 1 is a block diagram showing a functional configuration of an OS switching device when a module such as encryption is installed in the OS.

  The OS switching device includes an OS switching unit 100 and OSs 200 and 300.

  The OSs 200 and 300 hold OS stop units 201 and 301 for setting the OS in a suspended state and OS starting units 202 and 302 for returning the OS from a suspended state to an operating state.

  The OS 200 further includes an exception processing unit 210, a memory management unit 220, a secret generation unit 212, a key generation unit 213, an encryption / decryption unit 214, an integrity verification unit 215, and a read-only storage unit 216. A failure recovery unit 217 and an information holding unit 230.

  The exception processing unit 210 performs exception processing in the kernel. The exception processing unit 210 mounts a secret calculation unit 211 therein. The secret calculation unit 211 implemented in the exception processing unit 210 performs a calculation on the secret.

  The memory management unit 220 manages the correspondence between physical memory and logical memory in the kernel. The memory management unit 220 includes a duplicate memory management unit 221 and an absolute memory address management unit 222. The duplicate memory management unit 221 maps data for generating a secret used in the secret generation unit 212 to a plurality of locations on the virtual memory. The absolute memory address management unit 222 manages the absolute memory address of the data so that the secret generation unit 212 designates the data used to generate the secret by the absolute address on the virtual memory.

  The secret generation unit 212 generates a secret using the calculation function of the secret calculation unit 211.

  The key generation unit 213 generates an encryption / decryption key using the secret obtained as an output result of the secret generation unit 212.

  The encryption / decryption unit 214 performs encryption and decryption using the key obtained by the key generation unit 213.

  The integrity verification unit 215 creates and holds data for integrity verification using the secret obtained by the secret generation unit 212, and performs integrity verification.

  The read-only storage unit 216 stores data and codes in the OS.

  The failure recovery unit 217 performs recovery when falsification or failure is detected as the verification result of the integrity verification unit 215.

  The information holding unit 230 holds data and codes used by the OS 200 kernel and userland programs. The information holding unit 230 includes a confidential information holding unit 231. The confidential information holding unit 231 holds confidential information that needs to be prevented from being read or falsified.

  Although not shown, the OS 200 may further include a hardware assist obfuscation unit that performs hardware assist obfuscation using the secret calculated by the secret calculation unit 211.

  The exception processing unit 210 means exception processing in the kernel, and is an exception handler function that performs processing for exceptions such as page faults and division by zero. By installing the secret calculation unit 211 in the exception processing unit 210, analysis from the OS 300 becomes difficult. When the secret generation unit 212 generates a secret, an exception handler of the exception processing unit 210 is called. For example, a TLB (Translation Look-aside Buffer) entry in the memory management unit 220 is controlled by the OS 200. Erase when moving. Thereby, when the secret generation unit 212 generates a secret, the secret calculation unit 211 in the exception processing unit 210 is always executed. However, when attempting to reproduce the secret from the OS 300, simply executing the code does not cause exception processing, and the secret calculation unit 211 is not called, and thus the correct encryption / decryption key cannot be obtained. As the original data for generating a secret in the secret generation unit 212, for example, an address on the virtual memory of the function itself that generates the secret, a return address from this function, and a pseudo-random number can be used. In general, the return address of a function is obtained by specifying a memory address one word smaller from the stack pointer. Instead of implementing this processing as it is, an alias to the return address of the function is added as a TLB entry in the memory management unit 220 on the virtual memory. An alias is an entry for one page of memory in which virtual memory and physical memory are mapped so as to point to the same physical memory as the return address of the function. When specifying the return address of the function, by specifying the aliased virtual address, it is not explicitly indicated that the return address of the function is used, and it becomes difficult to reproduce the secret in the OS 300. . As a premise for this, by mounting the OS 200 so that the operation in the OS stop unit 201 becomes decisive, the state of the virtual memory stack in the memory management unit 220 is always the same during the OS suspend process. is required.

  FIG. 2 is a block diagram showing a functional configuration of the OS switching device when a module such as encryption is installed in the OS switching unit.

  The OS switching device is composed of modules having the same functions as those shown in FIG. A different point from the OS switching device shown in FIG. 1 is that the OS switching unit 600 includes many functions included in the OS 700 (OS 200 in FIG. 1).

  The OS switching unit 600 includes an exception processing unit 710, a secret calculation unit 711, a secret generation unit 712, a key generation unit 713, an encryption / decryption unit 714, an integrity verification unit 715, a read-only storage unit 716, a failure recovery unit 717, The memory management unit 720 includes a duplicate memory management unit 721 and an absolute memory address management unit 722.

  Each function arranged in the OS switching unit 600, an OS switching processing unit 601, an exception processing unit 710, a secret calculation unit 711, a secret generation unit 712, a key generation unit 713, an encryption / decryption unit 714, an integrity verification unit 715, The read-only storage unit 716, the failure recovery unit 717, the memory management unit 720, the duplicate memory management unit 721, and the absolute memory address management unit 722 have the functions, OS switching processing unit 101, exception processing unit 210, secret calculation shown in FIG. Unit 211, secret generation unit 212, key generation unit 213, encryption / decryption unit 214, integrity verification unit 215, read-only storage unit 216, failure recovery unit 217, memory management unit 220, duplicate memory management unit 221, absolute memory Since it is the same as that of the address management unit 222, the description is omitted here.

  Also, each function arranged in the OS 700, the OS stop unit 701, the OS start unit 702, the information holding unit 730, and the confidential information holding unit 731 are the functions, OS stop unit 201, OS start unit 202, information Since it is the same as the holding unit 230 and the confidential information holding unit 231, description thereof is omitted here.

  Furthermore, each function, OS stop unit 801, and OS start unit 802 arranged in the OS 800 are the same as each function, OS stop unit 301, and OS start unit 302 shown in FIG.

(OS switching method)
Next, the OS switching method according to the present embodiment will be described.

  3 and 4 are flowcharts at the time of OS switching in the OS switching device shown in FIG.

  FIG. 3 shows an encryption procedure when the OS suspension unit 201 starts the OS suspend process, and FIG. 4 shows an integrity verification / decryption procedure when the OS startup unit 202 starts the OS startup process. Is shown.

  In FIG. 3, when the OS stop unit 201 starts the OS switching process (step 100), the secret generation unit 212 generates a secret that is a seed of an encryption key (step 101).

  Next, in the exception processing unit 210 set in advance so as to be called when a secret is generated, the secret calculation unit 211 performs an operation on the secret (step 102), and the key generation unit 213 determines the finally obtained secret. Generate an encryption key using.

  Next, the encryption / decryption unit 214 encrypts critical data and code in the OS or the entire OS using the obtained encryption key (step 103). When encrypting the entire OS, a method of shortening the calculation time by using simple encryption that simply calculates an exclusive OR may be used.

  Next, the integrity verification unit 215 generates integrity verification data for the encrypted data (step 104), and the OS switching processing unit 101 performs OS switching (step 105).

  Next, a processing procedure when the operation of another OS is completed and control returns to the original OS will be described with reference to FIG.

  First, in order to start the original OS, when the OS startup unit 202 starts OS switching processing (step 106), the secret generation unit 212 generates a secret that is a seed for decryption (step 107).

  Next, at the time of generating a secret, in the exception processing unit 210, the secret calculation unit 211 performs a secret calculation and reproduces the same secret as that used for encryption (step 108).

  Next, the integrity verification unit 215 verifies the integrity of the critical code or data or the entire memory using the integrity verification data generated in step 104 (step 109). The encryption / decryption unit 214 performs decryption (step 110). If the integrity verification fails and there is a possibility of falsification or failure, the failure recovery unit 217 performs recovery processing from the ROM or the like (step 112).

  When the decryption or restoration is completed in the correct state, the OS switching processing unit 101 switches the OS, starts the original OS, and completes the process (step 111).

  5 and 6 are flowcharts at the time of OS switching in the OS switching device shown in FIG. The processing contents are basically the same as the procedures shown in FIG. 3 and FIG. 4, and are different in that these processes are performed in the OS switching unit.

  FIG. 5 shows an encryption procedure when the OS suspension unit 701 starts the OS suspend process, and FIG. 6 shows an integrity verification / decryption procedure when the OS startup unit 702 starts the OS startup process. Is shown.

  In FIG. 5, when the OS stop unit 701 starts the OS switching process (step 200), the secret generation unit 712 generates a secret that serves as an encryption key seed (step 201).

  Next, in the exception processing unit 710 set in advance so as to be surely called when a secret is generated, the secret calculation unit 711 performs an operation on the secret (step 202), and the key generation unit 213 determines the finally obtained secret. Generate an encryption key using.

  Next, the encryption / decryption unit 214 encrypts critical data and code in the OS or the entire OS using the obtained encryption key (step 203). When encrypting the entire OS, a method of shortening the calculation time by using simple encryption that simply calculates an exclusive OR may be used.

  Next, the integrity verification unit 715 generates integrity verification data for the encrypted data (step 204), and the OS switching processing unit 601 switches the OS and starts an OS in another domain (step 204). 205).

  Next, a processing procedure when the operation of another OS is completed and control returns to the original OS will be described with reference to FIG.

  First, when the OS activation unit 702 starts OS switching processing to activate the original OS (step 206), the secret generation unit 712 generates a secret that serves as a key for decryption (step 207).

  Next, at the time of generating a secret, in the exception processing unit 710, the secret calculation unit 711 performs a secret calculation and reproduces the same secret as that used for encryption (step 208).

  Next, the integrity verification unit 715 verifies the integrity of the critical code or data or the entire memory using the integrity verification data generated in step 204 (step 209). The encryption / decryption unit 714 performs decryption (step 210). If the integrity verification fails and there is a possibility of falsification or failure, the failure recovery unit 717 performs recovery processing from the ROM or the like (step 212).

  When the decryption or restoration is completed in the correct state, the OS switching processing unit 601 switches the OS, starts another domain OS, and completes the process (step 211).

(Function and effect)
In the present embodiment, a Multi-OS environment is assumed in which two or more OSs are appropriately switched by the Switcher method and operate in a normal privilege mode.

  In the OS switching device and the OS switching method according to the present embodiment, a pseudo random number generator (Blackbox PRNG) that does not operate correctly when an attacking OS is executed is realized. By applying processing such as encryption / integrity assurance data addition to the important information storage part in the OS area that is transferred to the suspended state, using pseudo-random data generated from the PRNG It is possible to cope with attacks from the operating system. That is, according to the OS switching device and the OS switching method according to the present embodiment, it is possible to make it difficult to reproduce the secret by the attacking OS by executing the secret used for encryption and integrity in the exception processing of the kernel. . Further, by reproducing the memory of the return address used as the secret seed, it becomes difficult to reproduce the secret.

  In the OS switching device according to the present embodiment, the OS includes a confidential information holding unit that stores confidential information, and an encryption / decryption unit that encrypts and decrypts the confidential information stored in the confidential information holding unit. And a key generation unit that generates an encryption key to be used by the encryption / decryption unit using the secret calculated by the secret calculation unit. For this reason, when generating secrets (pseudo-random data) in the secret generator stored in the OS, the secret is calculated in the exception processing unit of the OS, thereby generating a secret that is difficult to reproduce by the attacking OS. be able to.

  The OS also includes an integrity verification unit that verifies the integrity of data or code. For this reason, the integrity of data or code can be further enhanced.

  The OS switching unit includes a confidential information holding unit that stores confidential information, and an encryption / decryption unit that encrypts and decrypts the confidential information stored in the confidential information holding unit, and is calculated in the secret calculation unit. And a key generation unit that generates an encryption key used by the encryption / decryption unit using the secret. For this reason, when secret (pseudo random number data) is generated in the secret generator stored in the OS switching unit, the secret is calculated in the exception processing unit of the OS switching unit, which is difficult to reproduce by the attacking OS. Can be generated.

  The OS switching unit includes an integrity verification unit that verifies the integrity of data or code. For this reason, the integrity of data or code can be further enhanced.

  The OS switching device also includes a duplicate memory management unit that maps a plurality of secret generation units to the virtual address space of the memory. For this reason, it is possible to make the reproduction of the secret more difficult by mapping the original data used when generating the secret to a plurality of locations on the virtual memory and specifying a location away from the specific register.

  Further, the OS switching device includes an absolute memory address management unit that specifies data using an absolute memory address when the secret generation unit acquires data for generating a secret. For this reason, by specifying the original data for generating the secret using an alias on the virtual memory, it is possible to make the reproduction of the secret more difficult and further improve the safety.

  The OS switching device also includes a read-only storage unit that stores data and codes. For this reason, it is possible to prevent tampering attacks by executing secret generation and encryption processing from the ROM.

  In addition, the OS switching device includes a failure recovery unit that detects falsification and recovers to a normal state. For this reason, by recovering from the ROM when tampering or failure is detected, it is possible to increase resistance against not only reading by the attacking OS but also tampering attacks.

  The OS also includes an integrity verification unit that verifies the integrity of the OS switching unit. For this reason, the integrity of the OS switching unit can be further enhanced.

  The OS switching unit includes an integrity verification unit that verifies the integrity of the OS. This can further improve the integrity of the OS.

  In addition, the OS switching device includes a hardware assist obfuscation unit that performs hardware assist obfuscation. For this reason, the security can be further improved by using a secret that is difficult for the attacking OS to reproduce for hardware-assisted obfuscation.

(Other embodiments)
Although the present invention has been described according to the above-described embodiments, it should not be understood that the descriptions and drawings constituting a part of this disclosure limit the present invention. From this disclosure, various alternative embodiments, examples and operational techniques will be apparent to those skilled in the art.

  For example, in FIGS. 1 and 2, the OS switching device having two OSs has been described. However, the number of OSs is not limited to this, and the present invention may be applied to devices that switch three or more OSs. Of course.

  As described above, the present invention naturally includes various embodiments not described herein. Therefore, the technical scope of the present invention is defined only by the invention specifying matters according to the scope of claims reasonable from the above description.

It is a functional block diagram which shows the OS switching device which concerns on this embodiment (the 1). It is a functional block diagram which shows the OS switching device which concerns on this embodiment (the 2). It is a flowchart which shows the OS switching method which concerns on this embodiment (the 1). It is a flowchart which shows the OS switching method which concerns on this embodiment (the 2). It is a flowchart which shows the OS switching method which concerns on this embodiment (the 3). It is a flowchart which shows the OS switching method which concerns on this embodiment (the 4).

Explanation of symbols

100, 600 ... OS switching unit 101, 601 ... OS switching processing unit 200, 300, 700, 800 ... OS
201, 301, 701, 801 ... OS stop unit 202, 302, 702, 802 ... OS activation unit 210, 710 ... Exception processing unit 211, 711 ... Secret calculation unit 212, 712 ... Secret generation unit 213, 713 ... Key generation unit 214, 714 ... encryption / decryption unit 215, 715 ... integrity verification unit 216, 716 ... read-only storage unit 217, 717 ... failure recovery unit 220, 720 ... memory management unit 221, 721 ... duplicate memory management unit 222, 722 ... Absolute memory address management unit 230, 730 ... Information holding unit 231, 731 ... Confidential information holding unit

Claims (7)

An OS switching device for switching and operating a plurality of OSs including an OS stopping unit that stops an OS and an OS starting unit that resumes execution of the OS,
An exception handling unit that performs exception handling;
A secret generator for generating a secret used to realize the security function;
Is mounted on the exception processing section, and secret computing unit for executing operations on the secret,
A confidential information holding unit for storing confidential information;
An encryption / decryption unit that encrypts and decrypts the confidential information stored in the confidential information holding unit;
A key generation unit that generates an encryption key to be used by the encryption / decryption unit using the secret calculated by the secret calculation unit;
A memory management unit for mapping data for generating the secret used in the secret generation unit to a plurality of locations on a virtual memory;
With
The exception processing unit is configured to transfer an entry in the memory management unit to another OS so that the exception handler of the exception processing unit is called when the secret is generated in the secret generation unit. Erase
The return address of the function that generates the secret is obtained by adding an alias to the return address of the function on the virtual memory as an entry in the memory management unit,
The OS switching apparatus , wherein the alias is an entry in which the virtual memory and the physical memory are mapped so as to point to the same physical memory as a return address of the function . OS switching device according to claim 1, characterized in that the integrity of further comprising a verification unit for verifying the integrity of the data or code. The OS switching device according to claim 1 , further comprising a read-only storage unit that stores the data and code. The OS switching device according to claim 3 , further comprising a failure recovery unit that detects falsification and recovers to a normal state. OS switching device according to claim 4, characterized in that it comprises the integrity verification unit for verifying the integrity of the previous SL OS further. The OS switching according to any one of claims 1 to 5 , further comprising a hardware-assisted obfuscation unit that performs hardware-assisted obfuscation using the secret calculated by the secret calculation unit. apparatus. A plurality of OS, is operated by switching an OS in the plurality of, an OS switching method for switching the control from one OS to another OS,
Generating a secret used to realize the security function ;
And performing an operation to the secret,
Encrypting and decrypting stored confidential information;
Generating an encryption key used in the step of performing the encryption and decryption using the calculated secret;
Mapping data for generating the secret to a plurality of locations on the virtual memory using a memory management unit;
Including
In the step of generating a secret, an entry in the memory management unit is deleted when control is transferred to another OS so that an exception handler of the exception processing unit is called when the secret is generated. ,
The return address of the function that generates the secret is obtained by adding an alias to the return address of the function on the virtual memory as an entry in the memory management unit,
The OS switching method , wherein the alias is an entry in which the virtual memory and the physical memory are mapped so as to point to the same physical memory as the return address of the function .

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